Fracture Resistance of Endodontically Treated Teeth: Three Walls versus Four Walls of Remaining Coronal Tooth Structure

Purpose: The purpose of this study was to evaluate the fracture resistance of endodontically treated teeth between those with four walls and those with three walls of remaining coronal tooth structure and the effect of the site of the missing coronal wall. Materials and Methods: Thirty-two endodontically treated second mandibular premolars were decoronated, leaving 3 mm above the cementoenamel junction (CEJ). A 0.5-mm-wide chamfer was prepared 1 mm above the CEJ. The teeth were randomly divided into four groups. Group 1 had four walls of coronal tooth structure, whereas groups 2, 3, and 4 had only three walls, missing the buccal, lingual, and mesial wall, respectively. The cast dowel and cores and crowns (Ni-Cr alloy) were cemented with zinc phosphate cement. A compressive load was applied 45 degrees to the long axis, 2 mm below the buccal cusp, with an Instron machine until failure at a crosshead speed of 5 mm/min. Failure load (kg) and mode of failure were recorded. Data were analyzed with one-way ANOVA and Scheffe tests (p < 0.05). Results: Group 1 had the highest fracture resistance (1190.3 +/- 110.5 kg), significantly different from the other groups (p < 0.05) (group 2: 578.5 +/- 197.4 kg; group 3: 786.6 +/- 132.8 kg; group 4: 785.4 +/- 289.9 kg). There were no significant differences among the test groups. The mode of failure in group 1 was a horizontal root fracture, whereas that of the other groups was either vertical or oblique fracture. Conclusions: Teeth with four walls of remaining coronal dentine had significantly higher fracture resistance than teeth with only three walls. The site of the missing coronal wall did not affect the fracture resistance of endodontically treated teeth.